1. Field of the Invention
The invention relates to an extrusion spring arm for aiding in the eruption of palatally impacted cuspids. More specifically, the invention relates to such an extrusion spring arm which is mountable on an archwire and activated by an elastic ligature.
2. Description of Prior Art
In the practice of orthodontics, the situation often arises where a patient may have one or both upper cuspids impacted. In cases where the impacted cuspids are palatally positioned, access to the cuspids, and the ability to guide the cuspid into its proper position in the dental arch may be difficult to obtain. What is needed in many, if not all cases, is an extrusive force.
Devices for providing such an extrusive force are known in the prior art as illustrated in, for example, U.S. Pat. No. 4,187,610, Ziegler, Feb. 12, 1980 and U.S. Pat. No. 4,869,667, Vardimon, Sept. 26, 1989.
The Ziegler patent teaches the use of a ligation chain illustrated in FIG. 1 of the patent. One end of the chain has a loop portion 12. In operation, the impacted tooth must be surgically exposed so that all of the crown can be accessed. The loop is then slipped over the tooth and past the crown. The chain is then twisted so that the diameter of the loop is decreased until the diameter of the loop is less than the diameter of the crown. To activate the force to erupt the tooth, an elastic is attached to one end of the eyelet 14 at one end thereof, and to either a band 30 of an adjacent tooth or to an archwire 32. The elastic is, of course, placed under tension. One of the disadvantages of the '610 patent is that the surgeon has to uncover quite a bit of the tooth in order to get the loop 12 over the whole crown. In addition, although the patent states at column 4, lines 4 to 13, that the chain can be subsequently painlessly removed, it seems that the free end of the wire passing around the tooth as the wire is being pulled out could possibly scratch an inside part of the patient.
The Vardimon patent teaches a magnetic approach for the same purpose. Referring to FIG. 1 of the patent, an intra-osseous (bony) magnetic unit 16 is bonded to the tip of the crown of an impacted tooth 12. An intra-oral magnetic unit 18 is disposed in a position to provide magnetic attaction to the magnetic unit 16 whereby to explode the impacted tooth. The intra-oral magnetic unit 18 is mounted on archwire 36 by means of a two-dimensional connector 34. The two-dimensional connector 34 permits adjustment of the intra-oral magnetic unit in that the portion 37 permits sliding along the archwire 36. The disadvantage of this arrangement is that the arch connector in the '667 patent is relatively complex. In addition, the magnetic force is not a flexible force in that it acts only in a single direction.
Also known in the art is U.S. Pat. No. 4,580,976, O'Meara, Apr. 8, 1986, which teaches a spring member 18 mounted on an archwire 12. However, the arrangement in the '976 patent does not relate to exploding or extruding an impacted tooth.